May 29, 2013
J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington@nasa.gov
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov
RELEASE: 13-157
NASA'S WISE MISSION FINDS LOST ASTEROID FAMILY MEMBERS
WASHINGTON -- Data from NASA's Wide-field Infrared Survey Explorer
(WISE) have led to a new and improved family tree for asteroids in
the main belt between Mars and Jupiter.
Astronomers used millions of infrared snapshots from the
asteroid-hunting portion of the WISE all-sky survey, called NEOWISE,
to identify 28 new asteroid families. The snapshots also helped place
thousands of previously hidden and uncategorized asteroids into
families for the first time. The findings are a critical step in
understanding the origins of asteroid families, and the collisions
thought to have created these rocky clans.
"NEOWISE has given us the data for a much more detailed look at the
evolution of asteroids throughout the solar system," said Lindley
Johnson, the program executive for the Near-Earth Object Observation
Program at NASA Headquarters in Washington. "This will help us trace
the NEOs back to their sources and understand how some of them have
migrated to orbits hazardous to the Earth."
The main asteroid belt is a major source of near-Earth objects (NEOs),
which are those asteroids and comets that come within 28 million
miles (45 million kilometers) of Earth's path around the sun. Some
near-Earth objects start out in stable orbits in the main asteroid
belt, until a collision or gravitational disturbance flings them
inward like flippers in a game of pinball.
The NEOWISE team looked at about 120,000 main belt asteroids out of
the approximately 600,000 known. They found that about 38,000 of
these objects, roughly one third of the observed population, could be
assigned to 76 families, 28 of which are new. In addition, some
asteroids thought to belong to a particular family were reclassified.
An asteroid family is formed when a collision breaks apart a large
parent body into fragments of various sizes. Some collisions leave
giant craters. For example, the asteroid Vesta's southern hemisphere
was excavated by two large impacts. Other smash-ups are catastrophic,
shattering an object into numerous fragments, as was the case with
the Eos asteroid family. The cast-off pieces move together in packs,
traveling on the same path around the sun, but over time the pieces
become more and more spread out.
Previous knowledge of asteroid family lineages comes from observations
of their orbits. NEOWISE also looked at the asteroids' reflectivity
to identify family members.
Asteroids in the same family generally have similar mineral
composition and reflect similar amounts of light. Some families
consist of darker-colored, or duller, asteroids, while others are
made up of lighter-colored, or shinier, rocks. It is difficult to
distinguish between dark and light asteroids in visible light. A
large, dull asteroid can appear the same as a small, shiny one. The
dark asteroid reflects less light but has more total surface area, so
it appears brighter.
NEOWISE could distinguish between the dark and light asteroids because
it can detect infrared light, which reveals the heat of an object.
The larger the object, the more heat it gives off. When the size of
an asteroid can be measured, its true reflective properties can be
determined, and a group of asteroids once thought to belong to a
single family circling the sun in a similar orbit can be sorted into
distinct families.
"We're separating zebras from the gazelles," said Joseph Masiero of
NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., who is
lead author of a report on the new study that appears in the
Astrophysical Journal. "Before, family members were harder to tell
apart because they were traveling in nearby packs. But now we have a
better idea of which asteroid belongs to which family."
The next step for the team is to learn more about the original parent
bodies that spawned the families.
"It's as if you have shards from a broken vase, and you want to put it
back together to find out what happened," said Amy Mainzer, the
NEOWISE principal investigator at JPL. "Why did the asteroid belt
form in the first place and fail to become a planet? We are piecing
together our asteroids' history."
JPL, a division of the California of Technology in Pasadena, managed
and operated WISE for NASA's Science Mission Directorate. The
spacecraft was put into hibernation mode in 2011, after completing
its main objectives of scanning the entire sky twice.
More information is online at:
http://www.nasa.gov/wise
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